Review of gel systems for CO2 geological storage leakage and conformance control for enhanced oil recovery: Mechanisms, recent advances, and future perspectives

As a promising method of carbon emission reduction, carbon capture, utilization and storage (CCUS) is an important technology to achieve carbon neutrality. CO 2 geological storage is an indispensable part of CCUS technology, and it is also the most effective measure for long-term storage of CO 2 . However, when the injected high-pressure CO 2 encounters formation water, the pH value of the system will turn down to about 3.0 Wellbore cement degradation would be a problem because the internal structure would become loose under such a strong acid environment for a long period, and can ultimately lead to gas leakage. In addition, the complex temperature and pressure changes caused by the injection of CO 2 in the underground would also lead to micro-annulus between cement-casing and cement-formation rock. Due to the existence of hydrodynamic drive and buoyancy, the escape of CO 2 is inevitable, thus an appropriate sealant is necessary for the remediation of CO 2 leakage pathways. Gel systems are widely used as sealants in the field of oil and gas industry. Polymer gel is a kind of organic gel that can be modified by changing synthesis methods and synthetic ingredient, for instance, CO 2 -responsive gels are prepared by introducing CO 2 -sensitive groups on the macromolecular chain. Inorganic gels such as silicate gels are also an ideal sealants thanks to their advance chemical stability and injectability. This paper mainly reviewed recent advances of three types of gel systems for CO 2 leakage remediation, namely CO 2 responsive gels, silicate gels and polymer gels. Gelation process and characteristic of gel systems were also discussed. Finally, based on current research advances and existing problems, future prospect of gel systems used for CO 2 leakage remediation were proposed. • Gel systems for CO 2 geological storage leakage remediation were reviewed systematically. • Mechanical strength, temperature resistance and injectivity of the gel system were proposed to be enhanced. • The importance of gel application of CO 2 -responsive gel was emphasized.